1. Field of the Invention
The present invention relates to an optical component molding apparatus and molding method for injection molding of a high precision optical component. In particular, the present invention relates to a molding apparatus and a method for an optical component capable of reducing the molding time period, increasing the production efficiency and reducing the cost and the like using a smaller molding machine.
2. Description of Related Art
Recently, optical components such as objective lens are formed in a manner of injection molding using a plastic resin (refer to, for example, Patent Document 1 and Patent Document 2). Since, by molding optical components using a plastic, products of uniform configuration can be produced quickly, the molding is suitable for mass production thereof.
For example, as shown in FIG. 3, the molds for molding a plastic lens include a fixed mold 1 and a movable mold 2 capable of being brought into close contact with the fixed mold 1 and separated away therefrom. When the fixed mold 1 and the movable mold 2 are brought into close contact with each other, a void part 50 is formed. In a state that the both molds are in a close contact with each other, molten resin is injected into the void part 50 via a runner 52 and a gate 51 in this order. After the resin has solidified, the movable mold 2 is separated away from the fixed mold 1, and a molded item of a plastic lens is ejected and demolded. Thus, a plurality of plastic lenses are formed simultaneously.
Optical instruments utilizing the plastic lens have a tendency toward miniaturization and higher performance from year to year. Accompanying this, requests for miniaturization and higher precision of the plastic lens are also increasing.
Conventionally, for example, an optical pick up device is used 10 for recording/reading with a CD (Compact Disk) only. However, the application of the optical pick up device has expanded to compatibility between DVDs (Digital Versatile Disc) and CDs; and further, to the recording to DVDs (Digital Versatile Disc) and CDs. Recently, a standard of optical information recording medium, which enables information recording of higher density, is now under research and development. That is, an optical disk, which is capable of high density recording using a blue light of around 400 nm in wavelength, has been proposed. To achieve this, an objective lens of around 0.85 in number of aperture (NA) is required. Also, recently, in order to compensate spherical aberration, color aberration, temperature characteristics or the like, a minute structure such as diffraction grating is provided on the optical surface. And further, accompanying the miniaturization of the pick up device, the optical component itself has tended toward miniaturization.
As for an imaging optical system, a so called digital imaging device using an imaging optical element has been widely used. For example, the digital imaging device is used in video cameras, digital still cameras and the like. Particularly, a small size camera unit mounted on a portable electronic instrument such as a cellular phone is widely used. As for imaging devices mounted on these imaging instruments, CMOS (Complementary MOS) and CCD (Charge Coupled Device) are well known. These devices have also tended toward high density pixels and required accuracy levels for the imaging optical element have also been increasing.    [Patent Document 1] Japanese Published Unexamined Patent Application No. H11 42685, mold clamping force: 500 KN    [Patent Document 2] Japanese Published Unexamined Patent Application No. 2001 272501, mold clamping force: 300 KN
However, the following problems reside in the conventional molding apparatus. That is, conventionally, as the molding apparatus of optical components, relatively large size molding machines, in which the molds are brought into close contact with each other with a mold clamping force of a 300 KN to 500 KN class were used. Therefore, the strain of the molds is large when the molds are brought into close contact with each other and separated away therefrom. Accordingly, there arise the following problems. That is, a surface shift which is a displacement of the lens surface in the direction perpendicular to the optical axis a tilt which is an angular displacement of the lens surface with respect to the optical axis. Particularly, in the case of optical components, which require high precision, the occurrence of surface shift or tilt, etc. has large effect to the optical characteristics. Further, when the mold clamping force is large, the load against the molds is also large. Therefore, the molds tend to be deformed resulting in a molding failure.
Further, in a molding machine of which the clamping force is the 300 KN to 500 KN class, the clamping section becomes large in size. Also since a large amount of resin is required for injection, generally, the plasticization section and the injecting section are also large in size. In the case where a small item is molded using such a large machine, since the injection resolution is poor, fine adjustment of the molding conditions is hardly carried out. As a result, a transfer failure occasionally occurs. Further, since the size of the apparatus is large, a large installation space is required. There reside many factors of high cost such that a large power for driving the molding machine is required etc.